What best describes the functional residual capacity (FRC)?

  1. The FRC is approximately 10 ml/kg in a normal healthy adult and varies with training
  2. The FRC is composed of the inspiratory reserve volume and the closing capacity and varies with effort
  3. The FRC is measured by spirometry or pneumotachography and varies with temperature
  4. The FRC is the point of no flow at the end of a tidal breath